1. Field of the Invention
This invention relates to humidity control systems. More particularly, this invention relates to a humidity control system that automatically adjusts the level of humidity within a cargo container that is loaded with refrigerated cargo.
2. Description of the Prior Art
Humidity control systems are known in the art for controlling humidity levels within a cargo container that is loaded with a cargo being refrigerated via a container refrigeration unit. Conventional container refrigeration systems familiar to those skilled in the art of transport refrigeration have generally been more concerned with refrigerating a predetermined cargo than controlling its humidity. However, as cargo containers have become more sophisticated in design and more efficient in holding temperatures stable for longer periods of time, it has become increasingly more important to now also monitor and control the humidity levels within these cargo containers to ensure the cargo being transported arrives at its destination without even minor impairment. In view of the above, attempts have been made by those skilled in the art of transport refrigeration to design and manufacture systems which monitor humidity levels within loaded cargo containers and adjust the humidity accordingly. The problem is complicated by the fact that moisture is added to the nearly saturated air within a container and the humidity measuring device (sensor) is distant from the point of insertion of the moisture. One such system is manufactured by HMS-RYAN located in Redmond, Wash. The HMS-RYAN system monitors the humidity and subsequently adjusts the amount of moisture in the captured air within a sealed area by varying the speed of a metered water pump. Variable-speed pumping systems are disadvantageous in that it is difficult to maintain precise control of the container humidity level without continuously running the water pump. This process reduces the reliability of the humidity system as the water pump seals and internal moving parts, including motors and bearings, deteriorate more rapidly with continued long term usage. Further, the pumps tend to be noisy, particularly as they age, giving the end users the perception that the system is not working properly or otherwise is working inefficiently. The continuous running water pumps therefore require nuisance periodic maintenance or replacement. A continuous running water pump may also add an excessive quantity of moisture that will saturate packaging and condense upon produce.
Still needed, but not available with humidity monitoring and control systems presently known in the art is a humidity monitoring and control system that is capable of also reliably and efficiently establishing and maintaining precise humidity levels within a loaded cargo container, either as a stand-alone system or in combination with a transport refrigeration system.